ABC's Jim -- -- in Washington and reporting on this all -- good morning -- This morning toward the bombs that cause it's tragic wounds are actually. Quite small and portable like these -- devices they're easy to hide in the backpack. At this -- they're -- powerful enough to cause any structural damage but they're designed to wreak Havoc on the human body the flash. And the mind. That white smoke the damaging strapped. Telltale -- have an improvised explosive device. Seeing what they -- -- armored vehicles games and foot patrols in Iraq and Afghanistan. -- and he's like this when. Can cause quite a blast. But most office the smaller bombs as in busted. Are not strong enough to damage structures but they can be deadly beat anyone in the kills us. There's only one reason. To build an improvised explosive device and that's to kill or injure people. This demonstration shows the damage done by the shrapnel small pieces of metal often loaded inside the -- You can see and hear. Those dangerous projectiles exploding into the air. These people were close proximity to the vice want to -- off. That's we're gonna see the most catastrophic injuries. The actual blast of the Boston bomb was not strong mostly causing injuries from low flying debris. Leading authorities to call -- a small mobile IDD. The Times Square bomb two years ago was potentially much bigger carrying 250 pounds of ammonium nitrate a demonstration by the FBI. So that would have created a huge explosion if it would -- night. In the infamous underwear bomb designed to bring down an airplane may have been powerful enough to do it as this demonstration show. And unfortunately. Learning how to build these devices is public not. Good reason to hide -- easy to build it doesn't require a lot of skill. In fact experts say instructions to build bombs like the ones used in Boston can be found in the library or the Internet -- just a few clicks.

This transcript has been automatically generated and may not be 100% accurate.

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